Liver tissue consists of hexagonal unit structures called hepatic lobules. The hepatic lobule comprises hepatic vein (CV) in the center and portal triads (PT) in the periphery. In liver tissue, blood transports nutrients, hormones, waste products, and other signaling molecules from the portal triads to the hepatic vein through the pathway called sinusoid.
While blood is flowing through the sinusoid, liver cells are supplied nutritions via interaction with blood and exchange signaling molecules as well. So, those liver cells near the portal triads first consume such factors as nutritions, oxygen and hormones, and accordingly the concentration gradients of such factors are formed along the sinusoid. Due to the difference of in vivo environment, liver cells have functional heterogeneity according to the location where they belong, for example they have different functions such as ammonia detoxification, glucose and energy metabolism or external material metabolism.
In general, the regions to the hepatic vein are divided based on the portal triads as follows. The region around the portal triads is zone 1 (periportal area, PP), the region around the hepatic vein is zone 3 (perivenous area, PV), and the middle area is zone 2 (midzonal area). So, the zoning of hepatic lobule like the above is called liver zonation. Such division of the hepatic lobule is called liver zonation.
In the liver cells in zone 1 where oxygen-rich blood is flowing, such functions as gluconeogenesis, β-oxidation, cholesterol synthesis, ureogenesis, and the like are activated. These liver cells in zone 1 are susceptible to reactive oxygen, but display fast recovery. In the meantime, in the liver cells in zone 3 where oxygen-deficient blood is flowing, cytochrome P450 is highly activated so that not only drug metabolism is excellent but also such functions as lipogenesis, glycolysis, bile acid synthesis, and glutamine synthesis are activated. It is suggested thereby that the hepatic lobules are zoned and allotted with different functions to accomplish complicated liver functions simultaneously.
Studies on drug induced hepatotoxicity are an essential process to ensure drug safety in the development of new drugs. Various analysis methods have been developed for this purpose. For example, primary human hepatocytes are useful for the evaluation of hepatotoxicity in vitro by examining the expression of phase 1 and phase II enzymes. However, the primary human hepatocytes have disadvantages of unstable phenotypes in vitro, individual differences, difficulties in manipulation and high costs, because of which they have limitations in use. Thus, to overcome the problems above, various cell models capable of replacing the primary human hepatocytes have been studied. In relation to that, Korean Patent Publication No. 10-2015-0103431 describes a method for hepatotoxicity screening of immune based hepatotoxicity using human stem cell derived hepatocytes.
Although the hepatocyte model for toxicity evaluation has been dominantly studied to enhance the drug metabolism of hepatocytes themselves, the function of hepatic tissue has not been studied yet. However, studies of the hepatocyte model for toxicity evaluation have been mainly focused on the way to increase drug metabolism of hepatocytes themselves, and studies on the functions of the hepatic tissue according to the microenvironment of the hepatic tissue have not been progressed much.
Toxicity in hepatic tissue is induced under combined conditions. So, for the accurate evaluation and prediction of hepatotoxicity, it is necessary to develop a hepatotoxicity evaluation model reflecting not only the functions of hepatocytes themselves, but also the microenvironment of hepatic tissue. In particular, the drug metabolism environment differs according to the hepatic lobule zones, so that drug induced toxicity differs from the zones. Therefore, it is required to develop a microfabricated platform for mimicking the liver zonation reflecting such in vivo environment and an evaluating method of zone-specific hepatotoxicity using the same.
The present inventors tried to develop a cell model mimicking the in vivo environment of liver tissue. In the course of our study, the present inventors succeeded in preparing a microfabricated platform for mimicking the liver zonation by the processes of gelating hepatocytes by mixing the hepatocytes with a medium containing agarose in a tube, and forming a concentration gradient of CHIR in the gelated cells. And the present inventors further confirmed that the microfabricated platform for mimicking the liver zonation exhibited a difference in drug metabolism activity according to the zone and the result of the hepatotoxicity evaluation using the microfabricated platform for mimicking the liver zonation was consistent with the result of the hepatotoxicity evaluation using an animal model, leading to the completion of the present invention.